You have a span with background-color: #ffffff; as an inline style just after the section with class content.
This span though is wrapping other html elements. This is invalid markup as it is not a block level element. Make that a div instead (ensuring the closing tag is also a div too)
Thank you soooo much! That was driving me nuts.
Use firefox and install firebug. You can click the element with the inspection tool and see its CSS. You can easily identify you issues yourself
Also worth redoing the background and optimising that beter, takes ages to load even on fast net.